The subject invention relates generally to an apparatus and a process for ensuring a high quality crimp of an electrically conductive terminal to a wire. Electrical terminals include a wire mounting end which may be crimped into electrical and mechanical connection with a wire. The end of the wire may be stripped to expose the conductor therein. At least a first portion of the mounting end of the terminal will be crimped into electrical contact with the conductor of the wire. A second portion of the mounting end of the terminal may also be crimped into engagement with the insulated portion of the wire to contribute to strain relief of the electrical connection and to increase the force required to achieve a pull-out failure in the termination.
The crimping of the terminal to the wire is carried out in a crimping press. Prior art crimping presses take many forms, but most comprise at least one stationary tooling component, or anvil, and at least one movable tooling component, or punch. The stationary and movable components are cooperatively configured relative to one another to generate a secure crimping of the terminal to the wire. The movable component may be hydraulically or pneumatically powered or may comprise an electromechanical motor having a rotatable cam means for repetitively driving the movable tooling component.
Prior art crimp presses may also include means for feeding terminals and/or wires into appropriate positions relative to the tooling of the crimp press. More particularly, a plurality of terminals may be mounted to a carrier strip which facilitates the sequential feeding of terminals into and through the prior art crimp press. Wires also are urged into proximity to the tooling. When the terminal and the wire are properly positioned relative to one another, a crimping cycle will commence to crimp appropriate portions of the terminal around specified portions of the wire.
The degree of automation varies considerably from one prior art crimp press to the next. Many prior art crimp presses require the manual feeding of wires into a specified position relative to a terminal. Once the wire and terminal are properly positioned relative to one another and relative to the anvil, the operator will actuate a foot pedal which causes the crimp press punch to complete one cycle. Other prior art crimp presses include sensing means which actuate the punch of the crimp press in response to a sensed proper positioning of the end of the wire relative thereto. Still other prior art crimp presses include appropriate means for feeding, trimming, stripping and positioning the wires for automatic termination to crimpable terminals.
The quality of the crimped termination affects both the durability and the quality of the electrical connection. In particular, as noted above, a proper crimp will contribute to strain relief and will ensure that the normal mating or unmating forces exerted on the terminated wire do not damage the electrical connection. Additionally, the termination affects the ability of the wire and terminal to perform electrically. Preferably, the termination should be free of voids to ensure proper electrical performance. However, the exertion of too great a crimping force could significantly reduce the cross-sectional area or the wire in the vicinity of the crimp, and thereby afIect the strength and current carrying performance of the wire.
The quality of a crimped termination can be affected by many factors. For example, the crimp press tooling wears in response to the significant crimping forces exerted during termination. The wear of the crimp press tooling will effectively cause the opposed dies to be further from one another at the end of the movement of the dies toward one another. Thus, tooling wear causes a gradual increase in the crimp height. The increased crimp height decreases the pull-out force required for failure of the termination and decreases the quality of the crimp by eventually creating voids in the termination. In some situations, the crimp height may be too low for the particular wire and terminal. This may occur when the crimp tooling is changed or when the crimp press is adjusted in some manner. A crimp height that is too low can create the above described restrictions in current carrying capabilities and can break strands of the conductor.
Terminations of unacceptable quality may also occur in more highly automated prior art crimp presses. For example, an improper feeding of terminals or wires can result in multiple terminations to a single wire. This can seriously damage the expensive tooling and cause considerable down time for the crimp press. In other situations, a crimp cycle may be completed even though a terminal has not been properly fed into the crimp press. Some crimping operations require a terminal to be crimped to two wires or to the combination of at least one wire and a grounding clip. The improper feeding of one of the wires or a grounding clip may result in an unacceptable product that will not be identified until a much later stage in a manufacturing or assembly process.
The potential for unacceptable terminations requires the use of some sort of quality assurance. In less automated crimping operations, the quality assurance is achieved by a technician who visually inspects each termination. This visual inspection may be supplemented with pull-out tests on all or a statistically significant sample of the terminations. Visual inspection becomes less practical in more highly automated crimping operations. In these situations, greater reliance may be placed upon the time-consuming and destructive pull tests. The prior art also includes very complex and expensive optical scanning means for assessing the quality of a crimped termination. Optical scanning is shown in U.S. Pat. No. 4,555,799 which issued to Kodama et al on Nov. 26, 1985. The apparatus of U.S. Pat. No. 4,555,799 is operative to assess the profile of the crimped termination, and to optically compare that profile to an acceptable range of optical profiles for the particular crimped termination. This complex and costly apparatus is far from foolproof. In particular, a crimped termination may have the specified profile even though a portion of a multi-strand wire has not been incorporated into the crimp or even though more or fewer than the specified number of wires have been crimped.
The punch and anvil of a crimp press require periodic replacement in view of the unavoidable wear on these parts. Generally, the owner/operator of a crimp press will change the tooling after a specified number of crimping cycles. This approach, is based upon estimates of crimp tool life as determined by past experiences with similar tooling. In many instances, this approach leads to a change in crimp tooling before necessary or the use of crimp tooling after a change should have been effected.
It is known to employ strain gauges with metal stamping equipment. Strain gauges operate on the principal that each cycle of a stamping apparatus causes minute deformations of various structural members in the apparatus. The typical strain gauge employs a transducer mounted to or incorporated into a selected spaced apart location on the stamping apparatus. The transducer is connected to means for measuring voltage across the transducer. The voltage will vary proportionally in response to the dimensional changes which occur during operation of the stamping apparatus. For example, many strain gauges employ piezoelectric crystals operatively connected to the transducer of the strain gauge. The voltage across the piezoelectric crystals will vary in proportion to the dimension changes therein. Strain gauges for these purposes are available through International Measurement and Control Company (IMCO) of Frankfort, Ill.
The above described strain gauges have been used in stamping operations to sense an irregular operation of the stamping apparatus and to determine if the hardness of the stock material being presented to the stamping apparatus varies from specified hardness levels. Examples of prior art strain gauges for these purposes are shown in Reissue Patent No. Re. 30,298 which was reissued to Keller on June 3, 1980 and in U.S. Pat. No. 3,257,652 which issued to Foster on June 21, 1966. General discussions of strain gauges and their construction are included in U.S. Pat. No. 2,654,060 which issued to Stovall, Jr., et al on Sept. 29, 1953 and in U.S. Pat. No. 3,853,000 which issued to Barnett et al on Dec. 10, 1974.
In view of the above, it is an object of the subject invention to provide apparatus and method for assessing the quality of crimp terminations.
It is another object of the subject invention to provide apparatus and process for providing higher quality crimp terminations throughout a longer life of the crimp tooling.
It is a further object of the subject invention to provide automatic apparatus for performing nondestructive testing of crimped terminations as part of the normal crimp operations.
Still a further object of the subject invention is to provide accurate crimp quality assessment apparatus and process than can employ available crimping equipment and technology.
An additional object of the subject invention is to provide means and process for automatically adjusting crimp tooling to account for wear.